Lower electrode contact structure and method of forming the same

ABSTRACT

Lower electrode contact structures and methods of forming the same provide an interface having a large surface area between a lower electrode and the underlying layers. The lower electrode is in contact with a contact plug and an insulation layer in which the contact plug is buried. At least one supporting layer protrudes upright along the outer peripheral edge of the top surface of the contact plug. The interface between the lower electrode and the underlying layers is thus increased by the supporting layer(s) so that the lower electrode and the underlying layers will solidly adhere to each other.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional of application Ser. No. 10/634,898, filed Aug. 6,2003, now U.S. Pat. No. 6,861,690, which is incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to semiconductor memory devices and tomethods of forming the same. More specifically, the present inventionrelates to the structure of a semiconductor device whereat a lowerelectrode is disposed over underlying layers and to methods of formingthe same.

2. Description of the Related Art

The reduction in line widths of patterned portions of semiconductordevices, as facilitated by improvements in semiconductor devicefabricating techniques, is accompanied by decreases in the horizontaldimension and increases in the vertical dimension of various elements ofthe devices, such as capacitors. The surface area of the lowerelectrodes of such capacitors directly relates to the capacitance thatcan be offered by the capacitors. Therefore, a capacitor is formed witha large height so that the lower electrode thereof will have a largesurface area, whereby a certain value of capacitance can be provided.

That is, as semiconductor devices become more highly integrated within achip, the widths of the capacitors are correspondingly reduced.Accordingly, the heights thereof are increased to compensate for thedecrease in their width and still provide the same capacitance. As aresult, the area of the interface between the lower electrode and theunderlying layers is becoming smaller because the interface isdetermined by the width of the lower electrode. Thus, the adherence ofthe lower electrode to the underlying layers becomes weaker, so much sothat the lower electrode may separate from the underlying layers duringthe fabricating process. Consequently, adjacent lower electrodes maybecome electrically connected to each other.

FIG. 1 shows a conventional cylindrical lower electrode structure of acapacitor. Problems posed by the conventional lower electrode structureof a capacitor will be explained with reference to this figure. Acontact plug 18 penetrates an insulation layer 12 to electricallyconnect with an active region (not shown) of a semiconductor substrate10. A cylindrical lower electrode 28 is disposed on the insulation layer12 and the contact plug 18. As semiconductor devices become more highlyintegrated, the width W of the lower electrode 28 tends to decrease andthe height H thereof tends to increase. Therefore, an interface area CAdecreases where the lower electrode 28 and the underlying layers (i.e.,the contact plug 18 and the insulation layer 12) are in contact witheach other tends to decrease. Thus, the lower electrode may lean to oneside or collapse due to surface tension during a cleaning processcarried out after the process of forming the lower electrode. In such acase, adjacent lower electrodes may become electrically connected toeach other.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a lower electrodecontact structure in which the interface between the lower electrode andthe underlying layers is relatively large.

A lower electrode contact structure according to the present inventionincludes at least one electrode supporting layer protruding above theupper surface of an insulation layer in which a contact plug is buried.The electrode supporting layer(s) extends along the outer periphery ofthe upper surface of the contact plug. Therefore, the lower electrodeconforms to the surface morphology of the insulation layer, the contactplug, and the electrode supporting layer(s). Thus, the area of contactbetween the lower electrode and the underlying layers (i.e., the layerssupporting the lower electrode) is relatively large.

The at least one electrode supporting layer preferably comprises firstand second supporting layers. The first supporting layer extends alongthe outer peripheral edge of the top surface of the contact plug so asto protrude above the top of the insulation layer. The second supportinglayer is disposed on a portion of the insulation layer and on thecontact plug over inner and outer sidewalls of the first supportinglayer.

The contact structure may further comprise a sidewall spacer surroundingthe contact plug as interposed between the contact plug and theinsulation layer. The first electrode supporting layer is an extensionof the sidewall spacer. The first supporting layer and the sidewallspacer may be unitary or discrete. In the case of the latter, thesidewall spacer may be formed of silicon nitride and the firstsupporting layer may be formed of polysilicon.

The second electrode supporting layer of the contact structure may beformed of silicon nitride.

The contact structure may further comprise an etch stop layer disposedon the insulation layer around the lower electrode. The etch stop layermay be formed of silicon nitride. The thickness of the etch stop layeris identical to that of the second supporting layer.

A lower electrode contact structure may be fabricated according to thepresent invention as follows.

A contact hole is formed in a lower insulation layer disposed on asemiconductor substrate to expose an active region of the substrate. Asidewall spacer is formed along the sides of the contact hole. Next, arecessed contact plug is formed in the contact hole, i.e., so as tooccupy only a portion of the contact hole. A portion of the lowerinsulation layer is then removed such that a portion of the sidewallspacer protrudes above the resulting upper surface of the lowerinsulation layer. Finally, a lower electrode of a capacitor is formed onthe recessed contact plug, the protruding portion of the sidewallspacer, and that portion of the lower insulation layer that borders thecontact hole.

A lower electrode contact structure may also be fabricated according tothe present invention as follows.

A contact hole is formed in a lower insulation layer disposed on asemiconductor substrate to expose an active region of the substrate.Next, a recessed contact plug is formed in the contact hole, i.e., so asto occupy only a portion of the contact hole. Then a sidewall spacer isformed above the plug along the upper portion of the contact hole. Aportion of the lower insulation layer is then removed such that aportion of the sidewall spacer protrudes above the resulting uppersurface of the lower insulation layer. Finally, a lower electrode of acapacitor is formed on the recessed contact plug, the protruding portionof the sidewall spacer, and that portion of the lower insulation layerthat borders the contact hole.

In either case, the recessed contact plug is formed by depositingconductive material on the lower insulation layer so as to fill thecontact hole, and selectively etching the resulting layer of conductivematerial with respect to the lower insulation layer and the sidewallspacers until the upper surface of the layer of conductive materialbecomes situated beneath the level of the upper surface of theinsulation layer.

Also, the lower electrode is formed as follows. First, an etch stoplayer and an upper insulation layer are sequentially formed on top ofthe recessed contact plug, the protruding portion of the sidewallspacer, and the lower insulation layer. The upper insulation layer ispatterned to form an opening aligned with the recessed contact plug, thesidewall spacer, and a portion of the lower insulation layer thatborders the contact hole. The etch stop layer exposed through theopening is etched back. Then, an electrode material layer is formedalong the bottom and sides of the opening. A protecting insulation layeris formed on the electrode material layer so as to fill what remains ofthe opening therethrough. The protecting insulation layer and theelectrode material layer are planarized (etched) until the upper surfaceof the upper insulation layer is exposed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a conventional lowerelectrode structure of a semiconductor device, comprising a lowerelectrode of a capacitor.

FIG. 2 is a schematic cross-sectional view of an embodiment of a lowerelectrode contact structure in accordance with the present invention.

FIG. 3 is a schematic cross-sectional view of another embodiment of alower electrode contact structure in accordance with the presentinvention.

FIGS. 4A–4K are schematic cross-sectional views showing a method offorming the contact structure of FIG. 2.

FIGS. 5A–5I are schematic cross-sectional views showing a method offorming the contact structure of FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, throughout which like numbersdesignate like elements. Also, only one lower electrode is illustratedin the drawings for clarity.

Referring first to FIG. 2, a contact plug 180 a penetrates an insulationlayer 120 a to connect with an active region of a semiconductorsubstrate 100. The insulation layer 120 a surrounds the contact plug 180a. In the drawing, the contact plug 180 a is shown as having an uppersurface disposed beneath that of the insulation layer 120 a. However,the contact plug 180 a may project above the insulation layer 120 a ormay have an upper surface that is coplanar with that of the insulationlayer 120 a. Sidewall (insulation) spacers 160 a are interposed betweenthe contact plug 180 a and the insulation layer 120 a. The sidewallspacers 160 a may be of a material having an etch selectivity withrespect to the insulation layer 120 a. For example, the insulation layer120 a is a silicon oxide layer and the sidewall spacers 160 a are formedof silicon nitride.

A first supporting layer 160 b extends from the sidewall spacers 160 ato protrude over the tops of the insulation layer 120 a and the contactplug 180 a. The first supporting layer 160 b may be unitary with thesidewall spacers 160 a. That is to say, the first supporting layer 160 bmay be formed of the same material as the sidewall spacers 160 a.

A second supporting layer 200 b is disposed on inner and outer sidewallsof the exposed first supporting layer 160 b. The first and secondsupporting layers 160 b and 200 b together compose a structure forsupporting a lower electrode 280 a.

The lower electrode 280 a is disposed in contact with the contact plug180 a, the supporting layers 160 b and 200 b, and a portion of theinsulation layer 120 a around the contact plug 180 a. Therefore, thebottom of the lower electrode 280 a has a configuration corresponding tothe contour of this underlying structure, i.e., the area presented bythe contact plug 180 a, the supporting layers 160 b and 200 b, and theinsulation layer 120 a.

Specifically, the lower electrode 280 a comprises a sidewall 280 as anda bottom wall that is contiguous with the sidewall 280 as and contactsthe underlying structure. The bottom wall of the lower electrode 280 ais dented by the underlying structure. That is, the bottom wall of thelower electrode 280 a comprises parallel horizontal parts 280 ahdisposed on the insulation layer 120 a, the contact plug 180 a, and ontop surface of the supporting layers 160 b and 200 b, and vertical parts280 av disposed on sidewalls of the supporting layers 160 b and 200 band contiguous with the parallel horizontal parts 280 ah. As a result,the interface area between the lower electrode 280 a and the underlyingstructure is larger compared to that in a conventional contactstructure, by an amount corresponding to the contact areas defined bythe vertical parts 280 av.

An etch stop layer 200 a is disposed on the insulation layer 120 a. Theetch stop layer 200 a may be formed of the same material and may havepractically the same thickness as the second supporting layer 200 b.

The interface area between the lower electrode and the underlying layersof the lower electrode contact structure is relatively large so that thelower electrode tends to remain adhered to the underlying layers. Thatis, the underlying layers stably support the lower electrode.Accordingly, there is little possibility of the lower electrode cominginto contact with the lower electrode of an adjacent capacitor.

FIG. 3 shows another embodiment of a lower electrode contact structurein accordance with the present invention. This contact structure isidentical with the contact structure of FIG. 2 except for the insulationspacers. In this case, the first supporting layer 160 b may be formed ofsilicon nitride or a conductive material, for example, polysilicon.

In this embodiment, a contact plug 180 a extends through the entirety ofan insulation layer 120 so as to connect to an active region of asemiconductor substrate 100. A first supporting layer 160 b extendsalong the outer peripheral edge of the top surface of the contact plug180 a as protruding above the insulation layer 120 a and the contactplug 180 a. A second supporting layer 200 b is disposed on inner andouter sidewalls of the first supporting layer 160 b. A lower electrode280 a is disposed on the insulation layer 120 a, the contact plug 180 aand the supporting layers 160 b and 200 b.

A method of forming the lower electrode contact structure shown in FIG.2 will be explained hereinafter with reference to FIGS. 4A–4K. Thesubsequent processes, such as a device isolation process, a MOSFETprocess, and a bit line process are conventional per se and as such,will be omitted from the following detailed description.

Referring now to FIG. 4A, an insulation layer 120 is formed on asemiconductor substrate 100. The insulation layer 120 may be formed of,for example, silicon oxide. The insulation layer 120 is patterned toform a contact hole 140 exposing the active region (not shown) of thesemiconductor substrate 100. Therefore, the contact hole 140 has abottom defined by the active region and sides defined by the insulationlayer 120.

Referring to FIG. 4B, a material layer having an etch selectivity withrespect to the insulation layer 120, for example, a silicon nitridelayer 160, is formed on the sides and bottom of the contact hole 140 andon a top surface of the insulation layer 120 with a substantiallyuniform thickness.

Referring to FIG. 4C, an etch back process is performed on the resultantstructure. Portions of the silicon nitride layer 160 are removed fromthe bottom of the contact hole 140 and the top surface of the insulationlayer 120 so that a portion of the layer 160 remains only along thesides of the contact hole 140. Thus, sidewall (insulation) spacers 160 aare formed along the sides of the contact hole 140.

Referring to FIG. 4D, a plug conductive material layer 180 is formed onthe resultant structure to fill the contact hole 140. The conductivematerial layer 180 has an etch selectivity with respect to the sidewallspacers 160 a.

Referring to FIG. 4E, the conductive material layer 180 is etched toform a recessed contact plug 180 a filling only a portion of the contacthole 140. In other words, the top of the contact plug 180 a is situatedbeneath the top of the insulation layer 120, such that an upper part ofthe contact hole 140 a remains empty. The insulation layer 160 isdivided into two parts 160 a, 160 b located to either side of the topsurface of the recessed contact plug 180. The upper part 160 b of theinsulation layer, i.e., that part of the sidewall spacers disposed alongthe upper portion of the contact hole 140 a, will be referred tohereinafter as “a first supporting layer”.

Referring to FIG. 4F, the insulation layer 120 is etched. The etchingmay be carried out until the top surface of the insulation layer 120 abecomes coplanar with the top surface of the contact plug 180 a, orbecomes disposed at a level lower or higher than that of the uppersurface of the contact plug 180 a. In any case, inner and outersidewalls of the first supporting layer 160 b are exposed. The firstsupporting layer 160 b protrudes from a top surface of the etchedinsulation layer 120 a.

Referring to FIG. 4G, an etch stop layer 200 is formed on the insulationlayer 120 a, the contact plug 180 a, and the first supporting layer 160b. The etch stop layer 200 plays a role in stopping the etching in asubsequent process of patterning a sacrificial insulation layer. Inaddition, a portion of the etch stop layer 200 supports the lowerelectrode together with the first supporting layer 160 b, as will beexplained in more detail below.

Referring to FIG. 4H, a sacrificial insulation layer 220 that determinesthe height of the lower electrode is formed on the etch stop layer 200.A photoresist pattern 240 a is formed on the sacrificial insulationlayer 220. The photoresist pattern 240 a has an opening 260 atherethrough. The opening 260 a establishes the width of the lowerelectrode.

Referring to FIG. 4I, the sacrificial insulation layer 220 exposed bythe opening 260 a of the photoresist pattern 240 is etched using thephotoresist pattern 240 a as an etch mask. The etch stop layer 200serves to stop the etching process. Therefore, a trench 260 b is formedin the sacrificial insulation layer 220 a. The trench 260 b has a widthcorresponding to that of the opening 260 a defined by the photoresistpattern 240 a. The photoresist pattern 240 a is then removed.

Subsequently, the etch stop layer 200 exposed by the trench 260 b isetched back. Thus, the tops of the contact plug 180 a, the insulationlayer 120 a, and the first supporting layer 160 b are exposed and aportion of the etch stop layer remains on inner and outer sidewalls ofthe first supporting layer 160 b to constitute a second supporting layer200 b.

Referring to FIG. 4J, a lower electrode conductive layer 280 is formedalong the sacrificial insulation layer 220 a, the exposed portion of theinsulation layer 120 a, the contact plug 180 a, and the supportinglayers 200 b and 160 b. The lower electrode conductive layer 280 has auniform thickness. Subsequently, a protecting insulation layer 300 isformed on the lower conductive layer 280 to fill the entire trench 260.

Referring to FIG. 4K, the protecting insulation layer 300 and theconductive layer 280 are planarized (etched) to expose the top surfaceof the sacrificial insulation layer 220 a. Therefore, a lower electrode280 a is formed which is electrically isolated from the adjacent lowerelectrode(s).

The residual protecting insulation layer 300 a and the sacrificialinsulation layer 220 a are removed to expose inner and outer sidewallsand a bottom wall of the lower electrode 280 a, as illustrated in FIG.2. In this case, the lower electrode 280 a is firmly supported by theunderlying structure, such that the lower electrode 280 a will notcollapse or lean to one side during the removal of the insulation layers300 a and 220 a.

A dielectric layer and an electrode conductive layer are formed on theexposed lower electrode 280 a to complete the capacitor.

Subsequently, conventional fabricating processes including a metalinterconnection process, a passivation process and the like areperformed.

A method of fabricating the contact structure shown FIG. 3 will beexplained hereinafter with reference to FIGS. 5A–5I.

Referring first to FIG. 5A, an insulation layer 120 is formed on asemiconductor substrate 100. The insulation layer 120 is then patternedto form a contact hole 140 exposing an active region of thesemiconductor substrate 100.

Referring to FIG. 5B, a plug conductive material layer 180 is formed onthe insulation layer 120 to fill the entire contact hole 140.

Referring to FIG. 5C, the conductive material layer 180 is etched toform a recessed contact plug 180 a, i.e., a plug whose upper surface issituated beneath the top of the insulation layer 120. That is,conductive material is removed from the upper part of contact hole 140such that the resulting recessed contact plug 180 a occupies only alower part of the contact hole 140.

Referring to FIG. 5D, a supporting layer 160 is formed on sides andbottom of the upper part of the contact hole 140 a and on top of theinsulation layer 120. The supporting layer 160 is formed of materialhaving an etch selectivity with respect to the insulation layer 120, forexample, silicon nitride, polysilicon or the like. The supporting layer160 is conformal with respect to the underlying insulation layer 120 andthe contact plug 180 a.

Referring to FIG. 5E, an etch back process is carried out on thesupporting layer 160 to remove the supporting layer from the tops of thecontact plug 180 a and the insulation layer 120. The supporting layer160 is left only along the upper portion of the sides of the contacthole 140 a to form a first supporting layer 160 b.

Referring to FIG. 5F, an etch back process is carried out on theinsulation layer 120 to remove a portion of the insulating layer,thereby reducing the thickness thereof. As a result, the firstsupporting layer 160 b protrudes in a vertical direction beyond the topsof the etched insulation layer 120 a and the contact plug 180 a.

The remaining steps are performed in the same way as in the methoddescribed above. Briefly, referring to FIG. 5G, an etch stop layer 200is formed on the contact plug 180 a, the insulation layer 120 a, and thefirst supporting layer 160 b. Next, a sacrificial insulation layer 220and a photoresist pattern 240 a are formed on the etch stop layer 200.

Referring to FIG. 5H, a sacrificial insulation layer 220 exposed by theopening 260 a defined by the photoresist pattern 240 a is etched usingthe photoresist pattern 240 a as an etch mask. Therefore, a trench 260 bdelimiting the shape of a lower electrode is formed in the sacrificialinsulating layer 220 a. At this time, the etch stop layer 200 serves asan etch stop for the process of etching the sacrificial insulation layer220.

Referring to FIG. 5I, the exposed etch stop layer 200 is etched back.Therefore, the etch stop layer on top of the contact plug 180 a and theinsulation layer 120 a is removed. Thus, the etch stop layer is leftonly on inner and outer sidewalls of the first supporting layer 160 b toform a second supporting layer 200 b. Subsequently, a lower electrodeconductive layer 280 is formed on the exposed contact plug 180 a, thesupporting layers 160 b and 200 b, the insulation layer 120 a, and thesacrificial insulation layer 220 a. The subsequent processes areperformed in the same way as described in connection with the methodshown in FIGS. 4J and 4K.

In the methods described above, the lower electrode is formed as ahollow cylinder. However, the lower electrode may be formed as a solidcylinder. That is, a trench is formed in the upper sacrificialinsulation layer, and a layer of conductive material is deposited on theresulting structure to fill the trench. Then, the sacrificial insulationlayer may be removed. In this case, a protecting insulation layer is notnecessary.

According to the methods described above, the sidewall spacers and aportion of the etch stop layer are formed to protrude above the contactplug and to thereby support the lower electrode. Also, the interfacebetween the lower electrode and underlying layers is relatively large,such that the lower electrode and underlying layers can strongly adhereto one another. Therefore, the underlying layers stably support thelower electrode. In addition, the interface between the lower electrodeand the dielectric layer of the capacitor is correspondingly large.Consequently, the capacitor may provide a greater capacitance than aconventional capacitor of the same width.

Finally, although the present invention has been described in connectionwith the preferred embodiments thereof, various changes andmodifications may be made thereto without departing from the true spiritand scope of the invention as defined by the appended claims.

1. A method of forming a lower electrode contact structure of acapacitor, said method comprising: forming a contact hole through alower insulation layer disposed on a semiconductor substrate having anactive region so as to expose the active region; providing an insulatingmaterial on the sides of the contact hole to thereby form a sidewallspacer; forming a recessed contact plug in the contact hole and whichplug occupies only a lower portion of the contact hole; removing aportion of the lower insulation layer until the resulting upper surfacethereof is situated beneath the level of an upper portion of thesidewall spacer, whereby the upper portion of the sidewall spacerprotrudes above the resulting upper surface of the lower insulationlayer; and subsequently forming a lower electrode of a capacitor on therecessed contact plug, on said portion of the sidewall spacer protrudingabove the upper surface of the lower insulation layer, and on a portionof the upper surface of the lower insulation layer that borders thecontact hole.
 2. The method of claim 1, wherein said forming of therecessed contact plug comprises: forming a layer of conductive materialon the lower insulation layer so as to fill the contact hole; andselectively etching the layer of conductive material with respect to thelower insulation layer and the sidewall spacer so as to lower the uppersurface of the layer of conductive material beneath the level of theupper surface of the insulation layer.
 3. The method of claim 1, whereinsaid forming of the lower electrode comprises: sequentially forming anetch stop layer and an upper insulation layer on top of the recessedcontact plug, the sidewall spacer, and the lower insulation layer;patterning the upper insulation layer to form an opening aligned withthe recessed contact plug, the sidewall spacer, and the portion of theupper surface of the lower insulation layer that borders the contacthole; etching back the etch stop layer exposed by said opening; formingan electrode material layer at the bottom and along the sides of saidopening and on the upper insulation layer; forming a protectinginsulation layer on the electrode material layer so as to fill theopening; planarizing the protecting insulation layer and the electrodematerial layer until the upper insulation layer is exposed; andsubsequently removing the remainder of the protecting insulation layerand the upper insulation layer.
 4. The method of claim 3, wherein thesidewall spacer and the etch stop layer are formed of silicon nitride.